1. Field of the Invention
The present invention is related to an LED lighting device having multiple driving stages, and more particularly, to an LED lighting device having multiple driving stages for improving operational voltage range and line/load regulation.
2. Description of the Prior Art
Compared to traditional incandescent bulbs, light-emitting diodes (LEDs) are advantageous in low power consumption, long lifetime, small size, no warm-up time, fast reaction speed, and the ability to be manufactured as small or array devices. In addition to outdoor displays, traffic signs, and liquid crystal display (LCD) for various electronic devices such as mobile phones, notebook computers or personal digital assistants (PDAs), LEDs are also widely used as indoor/outdoor lighting devices in place of fluorescent of incandescent lamps.
An LED lighting device directly driven by a rectified alternative-current (AC) voltage usually adopts a plurality of LEDs coupled in series in order to provide required luminance. In a conventional method for driving an LED lighting device, the LEDs may be light up in stages in order to increase the effective operational voltage range. Line regulation is the ability of an LED lighting device to exhibit little change in brightness as the rectified AC voltage changes. Load regulation is the consistency in lamp-to-lamp brightness despite differences in the load voltage. Variations in line and load are similar in that a decrease in load voltage is effectively an increase in the rectified AC voltage (line voltage). Since the current is regulated independently in each stage of a prior art LED lighting device according the voltage established across each stage, the overall line/load regulation of the LED lighting device may not be able meet desired values. Therefore, there is a need for an LED lighting device capable of improving the effective operational voltage range and improving line/load regulation.